QtTaskTree::Group Class

class QtTaskTree::Group

Group represents the basic element for composing declarative recipes describing how to execute and handle a nested tree of asynchronous tasks. More...

Header:	`#include <qtasktree.h>`
CMake:	`find_package(Qt6 REQUIRED COMPONENTS TaskTree)` `target_link_libraries(mytarget PRIVATE Qt6::TaskTree)`
qmake:	`QT += tasktree`
Since:	Qt 6.11
Inherits:	QtTaskTree::ExecutableItem
Status:	Technical Preview

List of all members, including inherited members

Note: All functions in this class are reentrant.

Public Functions

	Group(const QtTaskTree::GroupItems &children)
	Group(std::initializer_list<QtTaskTree::GroupItem> children)

Detailed Description

Group is a container for other group items. It encloses child tasks into one unit, which is seen by the group's parent as a single, asynchronous task. Since Group is of the GroupItem type, it may also be a child of Group.

Insert child tasks into the group by using aliased custom task names, such as, QThreadFunctionTask<ResultType> or QNetworkReplyWrapperTask:

 const Group group {
     QNetworkReplyWrapperTask(...),
     QThreadFunctionTask<int>(...)
 };

You can customize the group's behavior by inserting the ExecutionMode or WorkflowPolicy items:

 const Group group {
     parallel,
     continueOnError,
     QNetworkReplyWrapperTask(...),
     QNetworkReplyWrapperTask(...)
 };

The group may contain nested groups:

 const Group group {
     finishAllAndSuccess,
     QNetworkReplyWrapperTask(...),
     Group {
         QNetworkReplyWrapperTask(...),
         Group {
             parallel,
             QNetworkReplyWrapperTask(...),
             QNetworkReplyWrapperTask(...),
         }
         QThreadFunctionTask<QString>(...)
     }
 };

The group may dynamically instantiate a custom storage structure, which may be used for inter-task data exchange:

 struct MyCustomStruct { QByteArray data; };

 Storage<MyCustomStruct> storage;

 const auto onFirstSetup = [](QNetworkReplyWrapper &task) { ... };
 const auto onFirstDone = [storage](const QNetworkReplyWrapper &task) {
     // storage-> gives a pointer to MyCustomStruct instance,
     // created dynamically by the running task tree.
     storage->data = task.reply()->readAll();
 };
 const auto onSecondSetup = [storage](QThreadFunction<QImage> &task) {
     // storage-> gives a pointer to MyCustomStruct. Since the group is sequential,
     // the stored MyCustomStruct was already updated inside the onFirstDone handler.
     const QByteArray storedData = storage->data;
 };

 const Group group {
     // When the group is entered by a running task tree, it creates MyCustomStruct
     // instance dynamically. It is later accessible from all handlers via
     // the *storage or storage-> operators.
     sequential,
     storage,
     QNetworkReplyWrapperTask(onFirstSetup, onFirstDone, CallDone::OnSuccess),
     QThreadFunctionTask<QImage>(onSecondSetup)
 };

Member Function Documentation

Group::Group(const QtTaskTree::GroupItems &children)

Constructs a group with a given list of children.

This constructor is useful when the child items of the group are not known at compile time, but later, at runtime:

 const QStringList sourceList = ...;

 GroupItems groupItems { parallel };

 for (const QString &source : sourceList) {
     const QNetworkReplyWrapperTask task(...); // use source for setup handler
     groupItems << task;
 }

 const Group group(groupItems);

Group::Group(std::initializer_list<QtTaskTree::GroupItem> children)

Constructs a group from std::initializer_list given by children.

This constructor is useful when all child items of the group are known at compile time:

 const Group group {
     finishAllAndSuccess,
     QNetworkReplyWrapperTask(...),
     Group {
         QNetworkReplyWrapperTask(...),
         Group {
             parallel,
             QNetworkReplyWrapperTask(...),
             QNetworkReplyWrapperTask(...),
         }
         QThreadFunctionTask<QString>(...)
     }
 };